Portable devices routinely depend upon batteries as a power source. To ease battery replacement costs, rechargeable batteries have found wide utility in powering contemporary consumer and business products. For example, nickel cadmium (Ni--Cad) batteries may be repeatedly used to energize computers, radios, pagers, and other such devices. As is well known, rechargeable batteries may be readily reenergized after use (i.e., after discharge) via a battery charger.
Depending on their chemistry, rechargeable batteries come in many varieties with each battery type requiring its own charging procedure. Such varieties include lead acid battery, Ni--Cad and Nickel Metal Hydride. For example, a lead acid battery requires a constant voltage charge procedure where the battery voltage is maintained constant throughout the charging process. On the other hand a Ni--Cad battery requires a constant current charging procedure where the charge current supplied to the battery is maintained constant. Also, at the same time, a Ni--Cad battery charging procedure differs from a Nickel Metal Hydride (Ni--MH) battery, in that, the battery voltage at which the charging process is stopped is different for a Ni--Cad battery than it is for a Ni--MH battery. Furthermore, the battery charging procedure may be dependent on non-chemical parameters, such battery capacity and the battery cell temperature. Battery capacity informs the charger as to how much current should be supplied to the battery. For example, the charger would provide a charge current at a substantially higher charge rate to a battery having 1600 mAHour capacity than to one having 900 mAHour capacity. The cell temperature, among other things, informs the charger when to stop charging to avoid battery explosion. Generally, the temperature information are relayed to the battery via a thermistor positioned near the battery cells.
More advanced battery packages utilize a memory device for storing certain battery related information. Koeneck in the U.S. Pat. No. 4,737,702 discloses a battery charging control system in which a memory device positioned in a battery pack stores information relating to operational history of the battery. Also, U.S. Pat. No. 4,387,344 issued to Loper discloses a battery monitor circuit for monitoring and storing in a memory device, digital data representing the power supplied by a battery.
Conventionally, the charging procedure is implemented via hardware or software in the charger itself. Charging procedure may be implemented through the charger hardware or it may be implemented through software by programming a microprocessor controlled charger. In modern microprocessor controlled chargers, a permanent storage medium, such as a Read-only-Memory (ROM), stores firmware containing instructions or procedure for charging the battery. For example, the constant voltage (or constant current) charging procedure may be programmed into the charger memory, and the charger controller executes the procedure to charge the battery.
However, with immense variety in charging procedures, a dilemma facing battery system manufacturers is the need for developing chargers to meet various charging requirements. This need has increased charger's development cost, design cycle time as well as its manufacturing cost.
Therefore, there is a need for a flexible battery charging system which allows for charging batteries with various charge requirements.